// m04 spawn: placing apples with the Random from random.js.
import { range, contains } from './util.js'
import { point, pointEquals, initialState } from './model.js'
import { advance } from './rules.js'
import { intBelow, run } from './random.js'

/** Every board cell not covered by the snake, row-major (y outer, x inner). */
export const freeCells = (state) =>
  range(state.height)
    .flatMap((y) => range(state.width).map((x) => point(x, y)))
    .filter((p) => !contains(state.snake, p, pointEquals))

/** Put an apple on a random free cell; a full board means the player has won. */
export const spawnApple = (state) => {
  if (state.apple !== null || state.status !== 'Playing') return state
  const cells = freeCells(state)
  if (cells.length === 0) return { ...state, status: 'Won' }
  const [i, seed] = run(intBelow(cells.length), state.seed)
  return { ...state, apple: cells[i], seed }
}

/** One game step: move the snake, then make sure there is an apple. */
export const tick = (state) => spawnApple(advance(state))

/** A fresh game with its first apple already placed. */
export const newGame = (seed) => spawnApple(initialState(seed))